<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>提升层级</title>
    <style>
	    .box1{
		    float:left;
			width:200px;
			height:200px;
			background-color:red;
			border:1px solid #000;
		}
		.box2{
		    width:300px;
			height:300px;
			background-color:blue;
			border:1px solid #000;
		}
		.bg1{
		    clear:both;
		}
		p{
		    color:green;
			font-size:20px;
		}
	</style>
</head>
<body>
    <div class="box1">div1</div>
    <div class="box2">div1</div>
	<div class="bg1"></div>
	<p>使用浮动可以提升元素的层级</p>
</body>
</html>